The observation that androgen-regulated genes are almost universally expressed in CRPC has prompted a search for processes that contribute to androgen receptor (AR) activation in the castrate environment. While pathways leading to prostate cancer growth and AR signaling may be entirely ligand-independent, many of the processes identified to date either still require or are enhanced by the presence of ligand. We hypothesize that castration-resistant prostate cancers arise through a process of metabolic adaptation involving the biosynthesis of AR ligands, rather than the selective propagation of rare tumor cells harboring advantageous genomic mutations/chromosomal alterations. Determining the key adaptive components has important implications for developing effective treatment strategies focused on modulating steroidogenic mechanisms. Thus, we also hypothesize that targeting components of androgen metabolism will inhibit the development or progression of CRPC. This proposal will i) evaluate the phenotype(s) of prostate tumor cells arising during metabolic adaptation to castration; and ii) define the AR ligand-generating pathways that emerge, providing novel data on critical nodes amenable to exploitation as therapeutic targets and for stratification of patients for appropriate interventions. We propose the following Specific Aims: AIM 1. Determine the contribution of steroid biosynthetic enzymes to the generation of intratumoral androgens and consequent tumor cell survival in CRPC. These studies will determine the frequency and mechanism(s) by which prostate tumors synthesize androgens de novo, determine the rate-limiting reactions, and determine if enhanced androgen metabolism contributes to tumor progression. AIM 2. Determine the mechanism(s) underlying the coordinate regulation of androgen biosynthetic enzymes and activation of the AR gene expression program in prostate cancers following the systemic reduction of androgens. AIM 3. Determine the therapeutic effectiveness of progressive inhibition of androgen metabolism and identify resistance mechanisms to metabolism-directed therapy in CRPC. These studies will determine the efficacy of progressively severe AR-pathway blockade on inhibiting intratumoral androgen production, evaluate the attendant effects on CRPC, and identify mechanisms leading to further tumor progression/resistance